BY DR. LAUDER BRUNTON. 430 



solved without decomposition. Neutralize them, and it is 

 precipitated. 



f Effect of Heat. At 170 C. it sublimes unchanged: a 

 higher temperature decomposes it. 



Put a little leucine into a dry test-tube and heat it gently. 

 It will rise in white clouds and be deposited on the cool part 

 of the tube. Heat the deposit strongly and a strong smell of 

 amylamine will be perceived. 



Decomposition. When decomposed by heat it yields C0 2 

 NH 3 , and amylamine. 



To show this put a portion of leucine into a hard glass bulb, 

 and connect this by means of India-rubber tubing with a glass 

 tube long enough to reach to the bottom of a test-tube. Pre- 

 pare two other similar pieces of glass tubing and three test- 

 tubes, the first of which should be about half filled with caus- 

 tic baryta solution, the second with Nessler's reagent, and the 

 third with water. Heat the bulb containing the leucine, apply- 

 ing the heat first to the upper part of the bulb and gradually 

 moving it downwards, so that as the leucine sublimes its vapor 

 may be strongly heated and decomposed. Pass the fumes into 

 the baryta solution, then disconnect the glass tubing, and after 

 attaching a clean piece, pass them into Nessler's reagent and 

 then into water. The baryta will be precipitated as white car- 

 bonate, the Nessler's reagent will become brown, showing the 

 presence of ammonia, and the water in the third test-tube will 

 acquire the peculiar smell of amylamine and an alkaline reac- 

 tion. Add to the barium solution a little nitric acid. It will 

 become clear and evolve gas, showing that the precipitate was 

 barium carbonate. A minute quantity only of Nil., is disen- 

 gaged when leucine is heated alone, and the coloration of Ness- 

 ler's reagent is therefore very slight. If a little lime and caus- 

 tic soda or potash are heated with the leucine much more NH 3 

 is given off. 



36. Preparation of Nessler's Reagent. Dissolve 4 

 grammes of potassium iodide in 250 cub. cent, of distilled 

 water. Set aside a few cub. cent, and add a cold saturated solu- 

 tion of mercuric chloride to the remainder, till the precipitate of 

 mercuric iodide is no longer dissolved on stirring. Add that 

 part of the potassium iodide solution which was set aside, to 

 the rest, so as to dissolve the remaining precipitate, and then 

 add mercuric chloride again very gradually, till a slight per- 

 manent precipitate is produced. If a few cub. cent, of the 

 potassium iodide solution were not set aside, great caution 

 would be required in adding the mercuric chloride so as to 

 avoid excess. Dissolve 150 grammes of potassium hydrate in 

 150 cub. cent, of distilled water, allow the solution to cool, and 

 add it gradually to the potassium iodide solution. Pour the 

 mixture into a measuring-glass or flask, and add distilled water 



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